9700 BIOLOGY. Mark schemes should be read in conjunction with the question paper and the Principal Examiner Report for Teachers.

Transcription

1 CAMBRIDGE INTERNATIONAL EXAMINATIONS GCE Advanced Subsidiary Level and GCE Advanced Level MARK SCHEME for the May/June 2013 series 9700 BIOLOGY 9700/53 Paper 5 (Planning, Analysis and Evaluation), maximum raw mark 30 This mark scheme is published as an aid to teachers and candidates, to indicate the requirements of the examination. It shows the basis on which Examiners were instructed to award marks. It does not indicate the details of the discussions that took place at an Examiners meeting before marking began, which would have considered the acceptability of alternative answers. Mark schemes should be read in conjunction with the question paper and the Principal Examiner Report for Teachers. Cambridge will not enter into discussions about these mark schemes. Cambridge is publishing the mark schemes for the May/June 2013 series for most IGCSE, GCE Advanced Level and Advanced Subsidiary Level components and some Ordinary Level components.

2 Page 2 Mark Scheme Syllabus Paper Mark schemes abbreviations: ; separates marking points / alternatives answers for the same point R do not allow A allow (for answers correctly cued by the question, or guidance for examiners) AW alternative wording (where responses vary more than usual) underline actual word given must be used by candidate (grammatical variants excepted) max indicates the maximum number of marks that can be given

3 Page 3 Mark Scheme Syllabus Paper 1 (a) (i) independent: concentration of GA ; dependent: ref. to the starch free, area / zone (around grains) ; (ii) 8 of: independent variable 1. ref. to method of diluting the (3 mmol dm 3 ) GA to give a minimum of (any) 5 dilutions ; 2. ref. to concentrations (other than 0) that fall in the range 3 mmol dm 3 to any value above zero with units ; 3. ref. to soaking grains in GA solutions for, min 24 hours / max 72 hours ; 4. ref. to a control using (distilled / deionised) water ; 5. ref. to stated incubation temperature ; ignore amount / quantity A diameter / radius / size A clear zone / brown zone / digested starch ignore ref. to amylase activity [2] P A seed / fruit / maize for any mark point in (a) ignore any ref. to time between soaking and putting maize onto agar plate 1. A series / serial / proportional / simple, dilution as method or description of method 2. minimum is 2 values that are not higher than 3 mmol dm 3 and are above zero 1 mmol dm 3 = 1000 µmol dm 3 1 µmol dm 3 = mmol dm 3 3. ignore if the range of GA is incorporated into agar plates If pre-soaked in water for 24h and then in GA, must be minimum of 1 hour GA 4. A description to allow comparison / AW 5. e.g. any one temp in the range C. A room temperature. R body temperature / 37 C

4 Page 4 Mark Scheme Syllabus Paper dependent variable 6. ref. to a suitable method of measuring the starch free area around the grains ; standardising variables (max 4): 7. ref. to using, same / stated number of, grains / halves, for each concentration ; 8. ref. to, stated / same, volume of each soaking solution / GA ; 9. ref. to method of keeping same incubation temperature ; 10. ref. to one stated time for incubation (of enzyme) ; 11. ref. to, same / stated, concentration of starch in agar ; 6. e.g. trace outline onto a grid / transparent grid / photograph and put on grid / cut out clear zone and put on grid, and count squares. OR use suitable apparatus to measure, diameter / radius, directly or from a grid and calculate area using πr 2 ignore metre ruler. A e.g. ruler / callipers / micrometer / eyepiece graticule 7. A one / a as same number ignore same size of grains / same amount of grains. A quantity for number 8. A idea of: all, submerged / covered 9. e.g. water bath / incubator / temperature controlled room / thermostatically controlled environment / environmental chamber / propagator / thermostat ignore air conditioning 10. A any value in the range hours. Actual value must be stated A left on, plate / agar as AW for incubate 11. A known time 12. ref. to same, volume / depth, of agar (in the Petri dishes) ; 13. covering to prevent, evaporation / contamination ;

5 Page 5 Mark Scheme Syllabus Paper safety: 14. ref. to, low risk investigation / any suitable safety precaution ; reliability: 15. ref. to replicates, and mean / to identify or eliminate anomalies ; (b) x-axis: concentration of GA and mmol dm -3 or µmol dm -3 ; y-axis: (mean) area of, clear zone / starch digested and mm 2 ; (c) (i) 3 of: 1. idea of areas irregular in shape ; 2. idea of edges of areas difficult to see ; 3. not sure how much GA embryo is also producing ; 14. e.g. cutting away from hands / using tile for cutting. ignore gloves for cutting. ref. to allergy / irritation, and, gloves / mask / eye protection R no risk 15. must be a minimum of 3 (data sets), allow as, original and 2 more / several A outliers for anomalies A average for mean [8] M A mmol or µmol, per dm 3 or mmol / dm 3 or µmol / dm 3 A (mean) diameter of clear zone / mm A cm 2 / cm A activity of amylase and arbitrary units / au labels correct no / incorrect, unit(s) = 1 max axes reversed, correct for labels and units = 1 max [2] D ignore ref. to replicates / repeats 1. A in terms of different diameters A in general terms like difficult to tell actual size 2. A in terms of edges overlapping or edges blurred / brown merging into blue / AW 3. A grain / fruit / seed for embryo 4. may be other, enzymes / chemicals, that hydrolyse the starch ;

6 Page 6 Mark Scheme Syllabus Paper 5. idea of: no way of quantifying amylase (leaving grain) ; 6. amylase / enzyme, may come from contamination ; 7. idea of: no method of quantifying the starch disappearance ; 8. ph may vary / AW ; (ii) method: any 1 2 of: 1. stated better method of measuring, (area / diameter) ; some brief detail of stated method ; 2. if overlap: separate plates / fewer grains per plate / larger plates ; able to distinguish edges more clearly / AW ; if blur : really cannot be improved = 2 marks ;; or do large sample ; minimises, effect / error / AW ; 3. idea of: separating the embryo from the grains (after soaking) ; idea of: measure area, without embryo present / with embryo on its own ; 4. idea of: extracting the amylase (from grain) ; idea of: repeat with just the extract and compare ; 5. A in terms of, not diffusing out / used inside / ref. to different surface area of (cut) grain / size of grain only in context of amylase not leaving grain or having different amounts of amylase 6. A coming from fungi / bacteria / coat of grain 7. idea of: do not know of the number of molecules of starch broken down. Look in context of the test being qualitative rather than quantitative. NOT rate ideas 1. e.g. use graticule on low power of microscope = 2 marks [3] E

7 Page 7 Mark Scheme Syllabus Paper 5. if in term of how much out / used up: idea of: extracting the amylase (from grain) ; idea of: repeat with just the extract and compare ; if in terms of different surface areas: idea of: measuring (surface) area ; idea of: either finding similar area or calculating per unit area ; 6. idea of: sterilising / disinfecting (grain / agar / dish /AW) ; detail of possible method ; 5. A remove endosperm repeat using embryo / AW 6. detail e.g. (named) disinfectant or sterile technique to, make plates / make up agar / handle grains or keep plate covered. 7. idea of: putting known concentrations of amylase on starch agar ; producing a calibration curve from areas measured ; 8. use a buffer ; to make up the agar (plates) ; [2] M Total: [17]

8 Page 8 Mark Scheme Syllabus Paper 2 (a) 3 of: 1. anaerobic bacteria increase with depth and aerobic bacteria decrease with depth ; 1. A general point but must relate to idea of depth 2. below m aerobic stay approximately the same and anaerobic continues to increase(slowly) ; 3. idea of: oxygen content of soil decreases with depth ; 4. idea that: anaerobic bacteria replace the aerobic bacteria as oxygen reduces / (most) aerobic unable to survive in low oxygen ; 3. A oxygen content decreases with time 4. A replacement in terms of succession / competition [3] C (b) (i) less activity of, dehydrogenase / enzyme ; (ii) 2 of: 1. temperature ; A less aerobic respiration R less dehydrogenase [1] E ignore ref. to oxygen 2. ph ; 3. idea of: time that determination was run for ; 4. (soil) moisture / water ; 5. substrate (in soil) ; 5. A (named) nutrients (in soil) [2] P (iii) idea of: (soil) without, (active) bacteria / active enzyme ; A heated / boiled / disinfected / sterilised / irradiated / AW, soil A (soil) with, dead / killed bacteria / denatured enzyme / enzyme removed A ref. to add an enzyme inhibitor A remove the bacteria from soil R killed enzyme / replace with (named) inert material [1] P

9 Page 9 Mark Scheme Syllabus Paper (c) (i) ref. to wide / long / big / AW, error bars, that indicate results are, less / not, reliable ; ref. to data ; A reverse argument A suitable AW for wide e.g. 6 years least reliable or 6 months / 3 years most reliable or more reliable in B than A at 6 years [2] D (ii) 6 months and 3 year, 6 months and 6 years both underlined / ringed ; error bars do not overlap ; A error bars do not cross / AW [2] D (d) idea of: graph of, dehydrogenase / enzyme, activity, against number of bacteria per gram (plotted) ; idea of: dehydrogenase / enzyme, activity located on graph and number of bacteria read from scale ; ignore orientation of graph. A if shown on a graph for 2 marks A idea of: comparing data against table to look for closest approximation = 1 mark max ignore compare unqualified [2] D Total: [13]